FIELD
[0001] Embodiments described herein relate generally to a nonaqueous electrolyte battery,
battery module and battery pack.
BACKGROUND
[0002] Nonaqueous electrolyte batteries including a negative electrode including a lithium
metal, lithium alloy, lithium compound, or carbonaceous material are expected as high
energy density batteries, and intensively studied and developed. Lithium ion batteries
including a positive electrode containing LiCoO
2 or LiMn
2O
4 as an active material, and a negative electrode containing a carbonaceous material
which absorbs and releases lithium ions are widely used in mobile devices.
[0003] On the other hand, when mounted on cars such as automobiles and trains, the components
of the positive and negative electrodes preferably have high chemical and electrochemical
stability, strength, and corrosion resistance, thereby providing high storage performance,
cycle performance, and long-term reliability of high output at high temperatures (60°C
or higher). Furthermore, high power performance and long cycle life performance at
low temperatures (cold climate areas) such as -40°C may be demanded.
[0004] On the other hand, for improving safety performance of nonaqueous electrolytes, incombustible
and nonvolatile electrolytic solutions are under development, but they are not still
in actual use because they can deteriorate the output properties, low temperature
performance, and long life performance. In addition, when mounted on a car or the
like, a lithium ion battery is difficult to replace a lead storage battery mounted
on the engine room of the car, and has problem with high temperature durability.
[0005] In a lithium ion battery, if the thickness of the negative electrode is decreased
to increase the density for increasing the output and capacity, the collector has
insufficient strength, so that the battery capacity, output performance, cycle life,
and reliability may be markedly limited. In addition, if the particle size of the
negative electrode active material is increased in place of decreasing the thickness
of the negative electrode, the interface resistance of the electrode increases, which
makes it more difficult to exploit high performance. In particular, at low temperatures
(for example, -20°C or lower), the rate of utilization of the active material decreases
and discharge is difficult.
[0006] US 2005/069777 A1 describes a nonaqueous electrolyte secondary battery including a case, a nonaqueous
electrolyte provided in the case, a positive electrode provided in the case, and a
negative electrode provided in the case, the negative electrode comprising a negative
electrode current collector and a negative electrode layer that is carried on the
negative electrode current collector and contains negative electrode active material
particles, and the negative electrode current collector comprising an aluminum foil
having an average crystal grain size of 50 µm or less or an aluminum alloy foil having
an average crystal grain size of 50 µm or less.
[0007] JP 2007-335308 A describes a nonaqueous electrolyte secondary battery equipped with an electrode group
with a cathode and an anode wound around through a separator into a flat spiral, the
cathode and the anode each containing a collector made of aluminum or an aluminum
alloy, at least one lead part connected to a long-side end part of the collector,
and an active material carried by the collector, satisfying the formula (L/W) ≤30
wherein, L is an effective length of a collector per lead part 1, and W is a width
in a short-side direction of the collector.
[0008] JP 2009038017 A describes an electrode for a nonaqueous electrolyte battery that is provided with
a current collector composed of aluminum foil or aluminum alloy foil and an active
substance containing layer which is formed on the current collector surface and contains
a bonding agent composed of an active substance, a conductive agent and an organic
polymer. The conductive agent contains carbon particles of which the aspect ratio
exceeds 1 and a of which has a long axis 1.05-1.50 times longer than a thickness of
the active substance containing layer, and moreover, one end in a longitudinal direction
of the carbon particles is embedded into the current collector in a depth of 20-50%
of the thickness of the current collector.
[0009] US 2013/040187 A1 describes a nonaqueous electrolyte battery that includes a negative electrode including
a current collector and a negative electrode active material having a Li ion insertion
potential not lower than 0.4V (vs. Li/Li+). The negative electrode has a porous structure.
A pore diameter distribution of the negative electrode as determined by a mercury
porosimetry, which includes a first peak having a mode diameter of 0.01 to 0.2 µm,
and a second peak having a mode diameter of 0.003 to 0.02 µm. A volume of pores having
a diameter of 0.01 to 0.2 µm as determined by the mercury porosimetry is 0.05 to 0.5
mL per gram of the negative electrode excluding the weight of the current collector.
A volume of pores having a diameter of 0.003 to 0.02 µm as determined by the mercury
porosimetry is 0.0001 to 0.02 mL per gram of the negative electrode excluding the
weight of the current collector.
[0010] JP 2001-143702 A describes a non-aqueous secondary battery cell which employs a secondary particle
formed by agglomerating primary particles of titanic acid lithium compound having
an average particle size of less than 1
µm and represented by the formula LiaTi3-aO4 (0<a<3), into granules having an average
particle size of 5 to 100
µm.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011]
FIG. 1 is a partially cutaway perspective view schematically showing the nonaqueous
electrolyte battery according to an embodiment;
FIG. 2 is an enlarged cross sectional view of the section A in FIG. 1;
FIG. 3 is a cross sectional view of the nonaqueous electrolyte battery according to
an embodiment;
FIG. 4 is an enlarged cross sectional view of the section B in FIG. 3;
FIG. 5 is an exploded perspective view of the battery pack according to an embodiment;
and
FIG. 6 is a block diagram showing the electric circuit of the battery pack in FIG.
5.
DETAILED DESCRIPTION
[0012] According to one embodiment, a nonaqueous electrolyte battery includes a container,
a nonaqueous electrolyte housed in the container, a positive electrode housed in the
container, and a negative electrode housed in the container. The positive electrode
includes an Al-containing positive electrode current collector, and a positive electrode
active material containing layer formed on the positive electrode current collector.
The negative electrode includes an Al-containing negative electrode current collector,
and a negative electrode active material containing layer formed on the negative electrode
current collector. The negative electrode active material containing layer includes
titanium-containing oxide particles having an average secondary particle of from 6
µm to 20 µm. The nonaqueous electrolyte battery satisfies the following formula (1):
wherein Lp is the thickness of the positive electrode current collector, and Ln is
the thickness of the negative electrode current collector. Furthermore, a difference
between the thickness Ln of the negative electrode current collector and the thickness
Lp of the positive electrode current collector is 1 µm or more
[0013] The embodiment also provides a battery module and a battery pack including the above-described
nonaqueous electrolyte battery.
(First embodiment)
[0014] In the negative electrode including the titanium-containing oxide particles having
an average secondary particle size of less than 5 µm, reductive decomposition of the
nonaqueous electrolyte proceeds at high temperatures (for example, 70°C or higher).
Therefore, the negative electrode has inferior cycle life performance at high temperatures.
If the average particle size of the secondary particles of titanium-containing oxide
particles is increased to exceed 5 µm thereby inhibiting reductive decomposition of
the nonaqueous electrolyte at high temperatures, the secondary particles are easily
cracked when the pressing force during manufacturing the negative electrode is increased
thereby increasing the negative electrode density (or negative electrode packing density).
If the secondary particles are cracked, many conductive paths between the primary
particles in the secondary particles are destroyed, so that the electron resistance
of the negative electrode increases. In addition, new surfaces are appeared by cracking
of the secondary particles accelerate reductive decomposition of the nonaqueous electrolyte
at high temperatures. Therefore, in place of increasing the negative electrode density,
the positive electrode density is increased by satisfying the relationship represented
by the above-described formula (1), more specifically, making the thickness of the
positive electrode current collector Lp smaller than the thickness of the negative
electrode current collector Ln. As a result of this, the necessity of increasing the
pressing force applied during the manufacturing process of the negative electrode
is avoided, so that cracking of the secondary particles of titanium-containing oxide
is inhibited. As a result of this, reductive decomposition of the nonaqueous electrolyte
at high temperatures is inhibited, without causing the increase in electron resistance
of the negative electrode. In addition, the increase in the positive electrode density
increases the adhesion strength between the positive electrode active material containing
layer and the positive electrode current collector, whereby the decrease in the adhesion
strength at high temperatures is inhibited, and the increase in the positive electrode
resistance at high temperatures is inhibited.
[0015] Accordingly, when the nonaqueous electrolyte battery is mounted on the engine room
of an automobile, the increases in the negative and positive electrode resistance
are inhibited under conditions including high rate charge-discharge cycle and large
current discharge at high temperatures (for example, 70°C or higher), so that the
cycle life performance and large current discharge performance at high temperatures
are improved.
[0016] When charge-discharge cycles are repeated at a high rate and a high temperature of
70°C or higher, the increase in the positive electrode resistance is caused by, for
example, oxidative decomposition of the nonaqueous electrolyte by the positive electrode
active material, and the decrease in adhesion between the positive electrode current
collector and positive electrode active material containing layer. On the other hand,
the increase in the negative electrode resistance is caused by, for example, the decrease
in electron conductivity between the titanium-containing oxide particle.
[0017] As a result of the study by the inventors, it was found that oxidative decomposition
of the nonaqueous electrolyte at high temperatures by the positive electrode active
material is inhibited when the nonaqueous electrolyte battery satisfies the following
the formula (2), where the maximum charging voltage of the positive electrode becomes
4 V (4 V vs. Li/Li
+) or less with reference to the Li potential.
wherein PW is the weight (g) of the positive electrode active material containing
layer, NW is the weight (g) of the negative electrode active material containing layer,
PC4 is the charging capacity per weight (mAh/g) when the maximum charging voltage
of the positive electrode is 4 V with reference to the Li potential (V vs. Li/Li
+), and NC is the charging capacity per weight (mAh/g) when the charging voltage of
the negative electrode is 1 V with reference to the Li potential (V vs. Li/Li
+).
[0018] PW is calculated by subtracting the weight of the positive electrode current collector
from the weight of the positive electrode weight, and NW is calculated by subtracting
the weight of the negative electrode current collector from the weight of the negative
electrode.
[0019] In the nonaqueous electrolyte battery satisfying the formula (2), the weight of the
positive electrode active material containing layer is greater than the weight of
the negative electrode active material, and the charging capacity per weight PC4 when
the maximum charging voltage of the positive electrode is 4 V with reference to the
Li potential (V vs. Li/Li
+) is smaller than the charging capacity per weight NC when the charging voltage of
the negative electrode is 1 V with reference to the Li potential (V vs. Li/Li
+). As a result of this, the end of charging depends on the potential change of the
negative electrode, and charging finishes before the charging potential of the positive
electrode reaches 4.2 V, so that resistance increase by oxidative decomposition of
the nonaqueous electrolyte by the positive electrode active material at high temperatures
is inhibited.
[0020] In the nonaqueous electrolyte battery satisfying the formula (2), the positive electrode
active material containing layer is thick, but the formula (1) is satisfied, so that
the adhesion strength between the positive electrode active material containing layer
and the positive electrode current collector is high. As a result of this, the electron
resistance between the positive electrode active material containing layer and the
positive electrode current collector is reduced, so that low resistance is maintained
even after the charge-discharge cycle.
[0021] In the titanium-containing oxide particles contained in the negative electrode, the
absorbing and releasing potential for Li is preferably from 1 to 3 V with reference
to the Li potential (V vs. Li/Li
+). In addition, the active material may be contained alone or in combination of two
or more. The titanium-containing oxide particles preferably contains one or more compounds
selected from the group consisting of lithium titanium oxide, titanium oxide, and
niobium titanium oxide. Examples of the lithium titanium oxide include lithium titanium
oxide having a spinel structure (for example, general formula Li
4/3+xTi
5/3O
4 (0 ≤ x ≤ 1.1)), lithium titanium oxide having a ramsdellite structure (for example,
Li
2+xTi
3O
7 (-1 ≤ x ≤ 3), Li
1+xTi
2O
4 (0 ≤ x ≤ 1), Li
1.1+xTi
1.8O
4 (0 ≤ x ≤ 1). Li
1.07+xTi
1.86O
4 (0 ≤ x ≤ 1), and Li
xTiO
2 (0 ≤ x ≤ 1).
[0022] Examples of the titanium oxide include those having a monoclinic system structure,
rutile structure, and an anatase structure. Examples of the titanium oxide having
a monoclinic system structure include those represented by the general formula Li
xTiO
2 (0 ≤ x, more preferably 0 ≤ x ≤ 1), i.e., the titanium oxide having a bronze structure
(B). The constitution of the titanium oxide having a rutile structure or anatase structure
before charging can be represented by TiO
2. Irreversible Li may remain in the titanium oxide after charge and discharge of the
battery, so that the titanium oxide after charge and discharge of the battery can
be represented by Li
xTiO
2 (0 ≤ x, more preferably 0 < x ≤ 1).
[0023] Examples of the niobium titanium oxide include those represented by Li
aTiM
bNb
2±βO
7±σ (0 ≤ a ≤ 5, 0 ≤ b ≤ 0.3, 0 ≤ β ≤ 0.3, 0 ≤ σ ≤ 0.3, wherein M is one or more elements
selected from the group consisting of Fe, V, Mo, and Ta).
[0024] The titanium-containing oxide particles are preferably lithium titanium oxide having
a spinel structure. Lithium titanium oxide having a spinel structure causes less volume
change during charge-discharge, and suppresses the resistance increase caused by reductive
decomposition of the nonaqueous electrolyte in the negative electrode, whereby the
cycle life performance is improved. In addition, aluminum or aluminum alloy foil may
be used in place of copper foil to make the negative electrode current collector,
thereby decreasing the weight and cost.
[0025] The average particle size (average diameter) of the primary particles of the titanium-containing
oxide particles is preferably 1 µm or less. As a result of this, improvements in the
discharge rate performance and high input performance (quick charge performance) are
expected. The reason is due to that, for example, the diffusion distance of lithium
ions in the active material is shortened, and the specific surface area increases.
The average particle size is more preferably from 0.1 to 0.8 µm.
[0026] The titanium-containing oxide particles may be the secondary particles alone or a
mixture of the primary and secondary particles. In order to further increase the density,
the proportion of the primary particles in the titanium-containing oxide particles
is preferably from 5 to 50% by volume. The average particle size (average diameter)
of the secondary particles is more preferably from 7 to 20 µm. When the average particle
size is within this range, a negative electrode having a high density is produced
while the pressing force during manufacturing the negative electrode is kept low,
and the stretch of the negative electrode current collector can be suppressed.
[0027] The positive electrode current collector is preferably aluminum foil or aluminum
alloy foil having an aluminum purity of 99% by weight or more, and a thickness Lp
of 20 µm or less. The aluminum purity is more preferably 99.5% by weight or more.
The thickness of the positive electrode current collector is preferably from 5 µm
to 15 µm. When the purity and thickness are within these ranges, the binding force
between the positive electrode active material containing layer and the positive electrode
current collector is improved, whereby the increase in electron resistance of the
positive electrode at high temperatures is inhibited. On the other hand, if a pure
aluminum foil collector having a purity of 100% by weight is used, the collector is
excessively stretcheded under a high pressing force, which can result in difficulty
in increasing the binding force between the positive electrode active material containing
layer and the positive electrode current collector.
[0028] A positive electrode active material is contained in the positive electrode active
material containing layer. Examples of the positive electrode active material include
lithium manganese composite oxides, lithium nickel composite oxides, lithium cobalt
aluminum composite oxides, lithium nickel cobalt manganese composite oxides, spinel
type lithium manganese nickel composite oxides, lithium manganese cobalt composite
oxides, olivine type lithium iron phosphates (for example, LiFePO
4), and olivine type lithium manganese phosphates (for example, LiMnPO
4). They can achieve a high positive electrode potential.
[0029] Examples of the lithium manganese composite oxide include Li
xMn
2O
4 and Li
xMnO
2 (0 ≤ x ≤ 1). Examples of the lithium nickel aluminum composite oxide include Li
xNi
1-yAl
yO
2 (0 ≤ x ≤ 1, 0 ≤ y ≤ 1 (more preferably 0 < y < 1)). Examples of the lithium cobalt
composite oxide include Li
xCoO
2 (0 ≤ x ≤ 1). Examples of the lithium nickel cobalt composite oxide include Li
xNi
1-y-zCo
yMn
zO
2 (0 ≤ x ≤ 1, 0 ≤ y ≤ 1 (more preferably 0 < y < 1), 0 ≤ z ≤ 1 (more preferably 0 <
z < 1)). Examples of the lithium manganese cobalt composite oxide include Li
xMn
yCo
1-yO
2 (0 ≤ x ≤ 1, 0 ≤ y ≤ 1 (more preferably 0 < y < 1)). Examples of the spinel lithium
manganese nickel composite oxide include Li
xMn
2-yNi
yO
4 (0 ≤ x ≤ 1, 0 ≤ y ≤ 2 (more preferably 0 < y < 2)). Examples of the lithium phosphate
having olivine structure include Li
xFePO
4, Li
xFe
1-yMn
yPO
4, Li
xCoPO
4 (0 ≤ x ≤ 1, 0 ≤ y ≤ 1 (more preferably 0 < y < 1)), and fluorinated iron sulfates
(for example, Li
xFeSO
4F (0 ≤ x ≤ 1)). When x is 1, Li is completely released from the positive electrode
active material by charging.
[0030] A lithium nickel aluminum composite oxide, lithium nickel cobalt manganese composite
oxide, or lithium manganese cobalt composite oxide inhibits the reaction with the
nonaqueous electrolyte at high temperatures, whereby the battery life is markedly
improved. The composite oxide represented by Li
xNi
1-y-zCo
yMn
zO
2 (0 ≤ x ≤ 1.1, 0 ≤ y ≤ 0.5 (more preferably 0 < y ≤ 0.5), 0 ≤ z ≤ 0.5 (more preferably
0 < z ≤ 0.5)) provides an excellent cycle life at high temperature.
[0031] The form of the nonaqueous electrolyte battery may be a rectangular battery, a cylindrical
battery, or a slim battery. The container may be, for example, a metal container or
a laminate film container including a metal layer and a resin layer. The laminate
film container is more preferred, thereby achieving the weight reduction.
[0032] The negative electrode, positive electrode, nonaqueous electrolyte, and container
are described below.
1) Negative electrode
[0033] The negative electrode includes a negative electrode current collector, and a negative
electrode active material containing layer which is supported on one side or both
sides of the negative electrode current collector, and contains a negative electrode
active material, a conductive agent, and a binder.
[0034] Examples of the Al-containing negative electrode current collector include aluminum
foil and aluminum alloy foil. The purity of aluminum may be from 98% to 100% by weight.
The purity of pure aluminum is 100% by weight. More preferably, the aluminum purity
is from 98.0 to 99.95% by weight. Examples of the metal other than aluminum composing
the aluminum alloy include one or more elements selected from the group consisting
of iron, magnesium, zinc, manganese, and silicon. For example, Al-Fe, Al-Mn, and Al-Mg
alloys can achieve higher strength than aluminum. On the other hand, the content of
the transition metal such as nickel or chromium in the aluminum and aluminum alloy
is preferably 100 ppm or less by weight (including 0 ppm by weight). For example,
the use of an Al-Cu alloy increases strength, but decreases corrosion resistance.
[0035] If the pressing force during manufacturing the negative electrode is reduced, thereby
avoiding cracking of the titanium-containing oxide particles having an average secondary
particle size of more than 5 µm, the stretch of the negative electrode current collector
during pressing can be reduced. As a result of this, a high negative electrode current
collector having an aluminum purity of 98% to 100% by weight and high electron conductivity
can be used.
[0036] For the thickness of the negative electrode current collector Ln, the final Ln after
pressing the negative electrode is preferably from 10 to 25 µm. When the Ln is within
this range, the stretch of the negative electrode current collector by pressing during
manufacturing the negative electrode is small, and the electron resistance of the
negative electrode current collector is low. When the Ln is greater than this range,
the thickness of the negative electrode increases. When the Ln is below this range,
cracking of the titanium-containing oxide particles increases, and the increase in
the electrode resistance and resistance increase during the high temperature cycle
may be accelerated.
[0037] The titanium-containing oxide particles having an average secondary particle size
of more than 5 µm are obtained by making an active material precursor having an average
particle size of 1 µm or less by the reaction and synthesis of raw active materials,
subjecting the active material precursor to sintering treatment, and then grinding
treatment using a grinder such as a ball mill or jet mill, and then the active material
precursor is aggregated in the sintering treatment to grow it into secondary particles
having a larger particle size. In addition, covering of the secondary particle surface
with a carbon material is preferred for reducing the negative electrode resistance.
It can be made by adding a carbon material precursor during manufacturing the secondary
particles, and sintering in an inert atmosphere at 500°C or higher.
[0038] The conductive agent for increasing the electron conductivity in the negative electrode
active material containing layer, and suppressing the contact resistance to the collector
may be a carbon material. Examples of the carbon material include acetylene black,
carbon black, coke, carbon fiber, and graphite.
[0039] Examples of the binder for binding the active material and conductive agent include
polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine rubber, styrene
butadiene rubber, and polyacrylic acid.
[0040] The proportions of the active material, conductive agent, and binder in negative
electrode are preferably from 80% to 95% by weight for the negative electrode active
material, from 3% to 18% by weight for the conductive agent, and from 2% to 7% by
weight for the binder. When the content of the conductive agent is 3% by weight or
more, the above-described effect is achieved, and when 18% by weight or less, decomposition
of the nonaqueous electrolyte on the conductive agent surface during storage at high
temperatures decreases. When the content of the binder is 2% by weight or more, a
sufficient electrode strength is obtained, and when 7% by weight or less, the electrically
insulating portion of the electrode is decreased.
[0041] The density of the negative electrode is preferably from 1.5 g/cm
3 to 5 g/cm
3. As a result of this, a high battery volume is obtained. Even more preferred range
is from 2 g/cm
3 to 4 g/cm
3.
[0042] The negative electrode is made by suspending a negative electrode active material,
a conductive agent, and a binder in an appropriate solvent, applying the suspension
to a negative electrode current collector, drying the suspension, and then pressing
the collector. The pressing force when manufacturing the negative electrode is preferably
from 0.1 ton/mm to 0.2 ton/mm. Within this preferred range, cracking of the secondary
particles is suppressed, and the percent stretch of the negative electrode current
collector is 10% or less.
2) Positive electrode
[0043] The positive electrode includes a positive electrode current collector, and a positive
electrode active material containing layer which is supported on one side or both
sides of the positive electrode current collector, and contains a positive electrode
active material, a conductive agent, and a binder.
[0044] Examples of the Al-containing positive electrode current collector include aluminum
foil and aluminum alloy foil. The purity of aluminum may be from 99% to 100% by weight.
The purity of pure aluminum is 100% by weight. The aluminum alloy preferably include
aluminum and one or more elements selected from the group consisting of iron, magnesium,
zinc, manganese, and silicon. For example, Al-Fe, Al-Mn, and Al-Mg alloys can achieve
a higher strength than aluminum. On the other hand, the content of the transition
metal such as nickel or chromium in the aluminum and aluminum alloy is preferably
100 ppm or less by weight (including 0 ppm by weight). For example, the use of an
Al-Cu alloy increase the strength, but decrease corrosion resistance. The aluminum
purity is more preferably from 99.0 to 99.99% by weight. Within this range, deterioration
of the high temperature cycle life caused by dissolution of impurity elements is reduced.
[0045] The thickness of the positive electrode current collector Lp is smaller than the
thickness of the negative electrode current collector Ln. The reason for this is that
the stretch of the positive electrode current collector by pressing is increased to
exceed that of the negative electrode current collector by increasing the pressing
force during manufacturing the positive electrode to exceed the pressing force during
manufacturing the negative electrode. As a result of this, adhesion between the positive
electrode active material containing layer and the positive electrode current collector
is improved to decrease resistance between them, the packing density of the positive
electrode active material containing layer is improved, and the thickness of the positive
electrode is reduced, so that the resistance increase by the charge-discharge cycle
at high temperatures is inhibited. As a result of this, the large current discharge
performance and cycle life performance at high temperatures are improved.
[0046] The thickness of the positive electrode current collector Lp is preferably 20 µm
or less. The final Lp of the positive electrode made through pressing is more preferably
from 5 to 15 µm. When the Lp is within this range, the stretch of the positive electrode
current collector by pressing is greater than that of the negative electrode current
collector, so that electron resistance between the positive electrode current collector
and the positive electrode active material containing layer is decreased. If the Lp
is beyond the range, electron resistance between the positive electrode current collector
and the positive electrode active material containing layer increases. If the Lp is
below the range, electric resistance of the positive electrode current collector increases.
[0047] Explanation about the positive electrode active material is as described above.
[0048] Examples of the conductive agent for increasing the electron conductivity and suppressing
the contact resistance to the collector include acetylene black, carbon black, and
graphite.
[0049] Examples of the binder for binding the active material with the conductive agent
include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluorine
rubber.
[0050] The proportions of the positive electrode active material, conductive agent, and
binder are preferably from 80% to 95% by weight for the positive electrode active
material, from 3% to 18% by weight for the conductive agent, and from 2% to 7% by
weight for the binder. When the proportion of the conductive agent is 3% by weight
or more, the above-described effect is achieved, and when 18% by weight or less, decomposition
of the nonaqueous electrolyte on the conductive agent surface during storage at high
temperatures is reduced. When the proportion of the binder is 2% by weight or more,
a sufficient electrode strength is achieved, and when 7% by weight or less, the electrically
insulating portion of the electrode is decreased.
[0051] The positive electrode is made by, for example, suspending a positive electrode active
material, a conductive agent, and a binder in an appropriate solvent, applying the
suspension to a positive electrode current collector, drying the suspension, and pressing
the collector. The pressing force is preferably from 0.15 ton/mm to 0.3 ton/mm. When
the pressing force is within this range, high adhesion (peel strength) is achieved
between the positive electrode active material containing layer and the positive electrode
current collector, and the percent stretch of the positive electrode current collector
is 20% or less.
3) Nonaqueous electrolyte
[0052] Examples of the nonaqueous electrolyte include a liquid nonaqueous electrolyte prepared
by dissolving an electrolyte in an organic solvent, a gelatinous nonaqueous electrolyte
prepared by complexing a liquid electrolyte with a polymer material, and a solid nonaqueous
electrolyte prepared by complexing a lithium salt electrolyte with a polymer material.
In addition, a room temperature molten salt (ionic liquid) containing lithium ions
may be used as a nonaqueous electrolyte.
[0053] The liquid state nonaqueous electrolyte is prepared by, for example, dissolving an
electrolyte in an organic solvent at a concentration of 0.5 to 2 mol/L.
[0054] Examples of the electrolyte include LiBF
4, LiPF
6, LiAsF
6, LiClO
4, LiCF
3SO
3, LiN(FSO
2)
2, LiN(CF
3SO
2)
2, LiN(C
2F
5SO
2)
2, Li(CF
3SO
2)
3C, and LiB[(OCO)
2]
2. The electrolyte may be used alone or in combination of two or more.
[0055] Examples of the organic solvent include cyclic carbonates such as propylene carbonate
(PC) or ethylene carbonate (EC), chain carbonates such as diethyl carbonate (DEC)
and dimethylcarbonate (DMC) or methylethyl carbonate (MEC), chain ethers such as dimethoxyethane
(DME) or diethoxyethane (DEE), cyclic ethers such as tetrahydrofuran (THF) or dioxolane
(DOX), γ-butyrolactone (GBL), α-methyl-γ-butyrolactone (MGBL), acetonitrile (AN),
and sulfolane (SL). These organic solvents may be used alone or in combination of
two or more thereof.
[0056] Examples of the more preferred electrolyte include LiPF
6, LiBF
4, LiN(FSO
2)
2 or LiB[(OCO)
2]
2. Examples of the more preferred organic solvent include propylene carbonate (PC),
ethylene carbonate (EC), diethyl carbonate (DEC), dimethylcarbonate (DMC), methylethyl
carbonate (MEC), γ-butyrolactone (GBL) or α-methyl-γ-butyrolactone (MGBL), which may
be used alone or in combination of two or more thereof.
[0057] Examples of the polymer material include polyvinylidene fluoride (PVdF), polyacrylonitrile
(PAN), and polyethylene oxide (PEO).
[0058] The room temperature molten salt (ionic liquid) preferably contains a lithium ion,
an organic cation, and an organic anion. In addition, the room temperature molten
salt is preferably a liquid at 100°C or lower, preferably at room temperature or lower.
4) Cladding member (container)
[0059] Examples of the cladding member include a laminate film container and a metal container.
The shape of the container conforms to the form of the nonaqueous electrolyte battery.
Examples of the form of the nonaqueous electrolyte battery include flat, square, cylindrical,
coin, button, sheet, laminated, and large-size batteries mounted on electric vehicles.
[0060] The thickness of the laminate film composing the container is preferably 0.5 mm or
less, more preferably 0.2 mm or less. In addition, the lower limit of the thickness
of the laminate film is preferably 0.01 mm.
[0061] On the other hand, the plate thickness of the metal container is more preferably
0.5 mm or less. In addition, the lower limit of the plate thickness of the metal container
is preferably 0.05 mm.
[0062] Examples of the laminate film include a multilayer film including a metal layer and
a resin layer covering the metal layer. For weight reduction, the metal layer is preferably
aluminum foil or aluminum alloy foil. The resin layer is provided for reinforcing
the metal layer, or for electrical insulation. The resin layer may be formed from
a polymer such as polypropylene (PP), polyethylene (PE), nylon, or polyethylene terephthalate
(PET).
[0063] The laminate film container is obtained by, for example, bonding laminate film by
heat sealing.
[0064] The metal container is preferably formed from aluminum or aluminum alloy. A container
made of an aluminum alloy has a high strength, so that sufficient mechanical strength
is assured even if the wall thickness of the container is decreased. As a result of
this, heat dissipation of the container is improved, whereby the increase of the battery
temperature is inhibited. In addition, the improvement in the energy density allows
weight and size reduction of the battery. These features are suitable for batteries
required to have high temperature resistance and a high energy density, such as in-vehicle
secondary batteries.
The aluminum alloy is preferably an alloy containing one or more elements selected
from the group consisting of magnesium, zinc, and silicon. On the other hand, the
content of transition metals such as iron, copper, nickel or chromium in the aluminum
and aluminum alloy is preferably 100 ppm or less by weight, respectively.
[0065] The metal container may be sealed by laser. As a result of this, the volume of the
sealing part is decreased, and the energy density is improved in comparison with that
of a laminate film container.
[0066] The nonaqueous electrolyte battery according to the embodiment may further include
a separator arranged between the positive and negative electrodes.
5) Separator
[0067] Examples of the separator include cellulose nonwoven fabric, synthetic resin nonwoven
fabric, a polyethylene porous film, and a polypropylene porous film. The thickness
of the separator may be from 5 to 30 µm.
[0068] The nonaqueous electrolyte battery according to the embodiment may be a nonaqueous
electrolyte battery of any form such as an angular, cylindrical, flat, slim, or coin
battery. FIGS. 1 and 2 show an example of the nonaqueous electrolyte battery including
a laminate film container. FIG. 1 is a partially cutaway perspective view schematically
showing the nonaqueous electrolyte battery according to an embodiment, and FIG. 2
is an enlarged cross sectional view of the section A in FIG. 1. These figures are
schematic views for explanation, and the shape, dimension, and ratio may be different
from those in an actual apparatus. The design may be appropriately changed in consideration
of the following explanation and known techniques.
[0069] A laminated electrode group 1 is housed in a bag container 2 made of laminate film
which includes a metal layer sandwiched between two layers of resin film. As shown
in FIG. 2, the laminated electrode group 1 has a structure wherein positive electrodes
3 and negative electrodes 4 are alternately laminated, with separators 5 sandwiched
therebetween. A plurality of positive electrodes 3 are present, and each of them includes
a positive electrode current collector 3a, and positive electrode active material
containing layers 3b formed on both sides of the positive electrode current collector
3a. A plurality of negative electrodes 4 are present, and each of them includes a
negative electrode current collector 4a, and negative electrode active material containing
layer 4b formed on both sides of the negative electrode current collector 4a. The
negative electrode current collector 4a of each of the negative electrodes 4 protrudes
from the positive electrode 3 at one side. The protruding negative electrode current
collector 4a is electrically connected to a negative electrode terminal strip 6. The
tip of the negative electrode terminal strip 6 is drawn out of the container 2. In
addition, not shown, the positive electrode current collector 3a of the positive electrode
3 protrudes from the negative electrode 4 at the side opposed to the protruding side
of the negative electrode current collector 4a. The positive electrode current collector
3a protruding from the negative electrode 4 is electrically connected to a positive
electrode terminal strip 7. The tip of the positive electrode terminal strip 7 locates
at the side opposite to the negative electrode terminal 6, and drawn out of the container
2 at the side.
[0070] In FIGS. 1 and 2, an example using a laminated electrode group is explained, but
the structure of the electrode group is not limited to a laminate, and may be a cylinder
or flat wound structure. For an example of a nonaqueous electrolyte battery including
a spiral electrode group, the structure is described with reference to FIGS. 3 and
4. FIG. 3 is a cross sectional view of a flat nonaqueous electrolyte secondary battery
10, and FIG. 4 is an enlarged cross sectional view of the section B of FIG. 3.
[0071] As shown in FIG. 3, a flat wound electrode group 1 is housed in a cladding member
2. The wound electrode group 1 has a structure including a positive electrode 3, a
negative electrode 4, and a separator 5 sandwiched between them, these components
being wound in a flat spiral. The nonaqueous electrolyte is retained in the wound
electrode group 1.
[0072] As shown in FIG. 4, the negative electrode 4 is located at the outermost periphery
of the wound electrode group 1, and a positive electrode 3 and a negative electrode
4 are alternately stacked with a separator 5 sandwiched therebetween, in the order
of the separator 5, positive electrode 3, separator 5, negative electrode 4, separator
5, positive electrode 3, and separator 5 at the inner periphery of the negative electrode
4. The negative electrode 4 includes a negative electrode current collector 4a and
a negative electrode active material containing layer 4b supported on the negative
electrode current collector 4a. In the area located at the outermost periphery of
the negative electrode 4, the negative electrode active material containing layer
4b is formed on only one side of the negative electrode current collector 4a. The
other negative electrode 4 includes the negative electrode active material containing
layers 4b formed on both sides of the negative electrode current collector 4a. The
positive electrode 3 includes the positive electrode current collector 3a, and one
or more positive electrode active material containing layer 3b supported on the positive
electrode current collector 3a.
[0073] As shown in FIG. 3, a positive electrode terminal 7 is electrically connected to
the positive electrode current collector 3a near the outer peripheral edge of the
wound electrode group 1. On the other hand, a negative electrode terminal strip 6
is electrically connected to the negative electrode current collector 4a near the
outer peripheral edge of the wound electrode group 1. The tips of the positive electrode
terminal 7 and negative electrode terminal 6 are drawn out of the cladding member
2 at the same side.
[0074] The nonaqueous electrolyte battery according to the first embodiment includes a negative
electrode containing titanium-containing oxide particles having an average secondary
particle size of from 6 µm to 20 µm and satisfies the formula (1), so that the high
rate charge-discharge cycle life performance and large current discharge performance
at high temperatures are improved. Therefore, a nonaqueous electrolyte battery useful
as a secondary battery alternative to a lead battery used as a power source of vehicle
starter, or as an in-vehicle secondary battery mounted on a hybrid car is provided.
(Second embodiment)
[0075] A second embodiment provides a battery module including nonaqueous electrolyte batteries
as unit cells, and a battery pack including the battery module. The nonaqueous electrolyte
battery may be the nonaqueous electrolyte battery of the first embodiment.
[0076] Examples of the battery module include those including a plurality of unit cells
which are electrically connected in series or parallel, and those including a unit
including a plurality of unit cells which are electrically connected in series, and
another unit including a plurality of unit cells which are electrically connected
in parallel.
[0077] Examples of the form of serial or parallel electrical connection of a plurality of
nonaqueous electrolyte batteries include serial or parallel electrical connection
of a plurality of batteries each having a container, and serial or parallel electrical
connection of a plurality of electrode groups housed in a common cabinet. According
to a specific example of the former, a plurality of nonaqueous electrolyte batteries
whose positive and negative electrode terminals are connected by a metal bus bar.
Examples of a material for the metal bus bar include aluminum, nickel, and copper.
According to a specific example of the latter, a plurality of electrode groups are
housed in one cabinet with electrochemically insulated by a diaphragm, and these electrode
groups are electrically connected in series. When the number of the batteries electrically
connected in series is from 5 to 7, an appropriate voltage compatibility is achieved
for a lead storage battery. A battery module including the units electrically and
serially connected six nonaqueous electrolyte batteries each having a positive electrode
containing a composite oxide represented by Li
xNi
1-y-zCo
yMn
zO
2 (0 ≤ x ≤ 1.1, 0 ≤ y ≤ 0.5, 0 ≤ z ≤ 0.5) provides an excellent cycle life at high
temperature.
[0078] A battery pack is described in detail with reference to FIGS. 5 and 6. A plurality
of unit cells 21 composed of the flat nonaqueous electrolyte battery shown in FIG.
3 are stacked in such a manner that a negative electrode terminal 6 and a positive
electrode terminal 7 extending out are oriented in the same direction, and bound by
adhesive tape 22 to make a battery module 23. These unit cells 21 are electrically
serially connected to each other as shown in FIG. 6.
[0079] A printed circuit board 24 is located opposed to a side of the unit cells 21 from
which the negative electrode terminal 6 and positive electrode terminal 7 are extended.
As shown in FIG. 6, a thermistor 25, a protective circuit 26, and an energizing terminal
27 to an external device are mounted on the printed circuit board 24. An insulating
plate (not shown) is mounted on a surface of the printed circuit board 24 opposite
to the battery module 23, thereby avoiding unnecessary connection with the line of
the battery module 23.
[0080] A positive electrode lead 28 is connected to the positive electrode terminal 7 located
on the lowermost layer of the battery module 23, and its tip is inserted into and
electrically connected to a positive electrode connector 29 of the printed circuit
board 24. A negative electrode lead 30 is connected to a negative electrode terminal
6 located on the uppermost layer of the battery module 23, and its tip is inserted
into and electrically connected to a negative electrode connector 31 of the printed
circuit board 24. These connectors 29 and 31 are connected to a protective circuit
26 through the lines 32 and 33 formed on the printed circuit board 24.
[0081] Thermistor 25 is used to detect the temperature of the unit cells 21. The detection
signal is sent to the protective circuit 26. The protective circuit 26 can shut down
a plus wiring 34a and a minus wiring 34b between the protective circuit 26 and the
energizing terminals 27 to an external instrument under a predetermined condition.
For example, the predetermined condition indicates when the detection temperature
of the thermistor 25 becomes a predetermined temperature or more. Or, the predetermined
condition indicates when the over-charge, over-discharge, and over-current of the
unit cells 21 are detected. The over-charge detection may be performed on each of
the unit cells 21 or the battery module. When each of the unit cells 21 is detected,
the cell voltage may be detected, or positive electrode or negative electrode potential
may be detected. In the case of the latter, a lithium electrode to be used as a reference
electrode is inserted into each of the unit cells 21. In the case of FIGS. 5 and 6,
wirings 35 for voltage detection are connected to the unit cells 21 and detection
signals are sent to the protective circuit 26 through the wirings 35.
[0082] Protective sheets 36 comprised of rubber or resin are arranged on three side planes
of the battery module 23 except the side plane in which the positive electrode terminal
7 and the negative electrode terminal 6 are protruded.
[0083] The battery module 23 is housed in a housing case 37 together with each of the protective
sheets 36 and the printed wiring board 24. That is, the protective sheets 36 are arranged
on both internal planes in a long side direction and on one of the internal plane
in a short side direction of the housing case 37. The printed wiring board 24 is arranged
on the other internal plane at the opposite side in a short side direction. The battery
module 23 is located in a space surrounded by the protective sheets 36 and the printed
wiring board 24. A lid 38 is attached to the upper plane of the housing case 37.
[0084] In order to fix the battery module 23, a heat-shrinkable tape may be used in place
of the adhesive tape 22. In this case, the battery module is bound by placing the
protective sheets on the both surfaces of the battery module, revolving the heat-shrinkable
tape, and thermally shrinking the heat-shrinkable tape.
[0085] In FIGS. 5 and 6, the form in which the unit cells 21 are connected in series is
shown. However, in order to increase the battery capacity, the cells may be connected
in parallel. Alternatively, the cells may be formed by combining series connection
and parallel connection. The assembled battery pack can be connected in series or
in parallel.
[0086] The embodiment of the battery pack is appropriately changed according to the use.
The battery pack according to the embodiment is used suitably for the application
which requires the excellent cycle characteristics at a high current. It is used specifically
as a power source for digital cameras, for vehicles such as two- or four-wheel hybrid
electric vehicles, for two- or four-wheel electric vehicles, and for assisted bicycles.
Particularly, it is suitably used as a battery for automobile use.
[0087] The second embodiment described above includes the nonaqueous electrolyte battery
of the first embodiment, so that a battery module and a battery pack having improved
high rate charge-discharge cycle life performance and large current discharge performance
at high temperatures are provided. Therefore, the battery module and battery pack
thus provided are suitable as a power source alternative to lead batteries used as
a power source starting a vehicle, or as in-vehicle secondary batteries mounted on
a hybrid car.
[Example]
[0088] The examples of the present invention are described below with reference to the above-described
drawings. The present invention will not be limited to the following examples, without
departing from the scope of the present invention.
(Example 1)
<Producing of negative electrode>
[0089] Lithium titanate (Li
4/3Ti
5/3O
4) powder as a negative electrode active material having an average secondary particle
size of 8 µm and an Li absorbing potential pf 1.55 V (vs. Li/Li
+), carbon powder as a conductive agent having an average particle size of 0.4 µm,
and polyvinylidene fluoride (PVdF) as a binder were mixed at a weight ratio of 90
: 7 : 3, and the mixture was dispersed in an n-methylpyrrolidone (NMP) solvent to
make a slurry.
[0090] The secondary and primary particle sizes of the active material were measured using
a laser diffraction particle size distribution analyzer (manufactured by Shimadzu
Co., Ltd., model number SALD-300) and an electron microscope. Firstly, about 0.1 g
of the sample was placed in, for example, a beaker, a surfactant and 1 to 2 mL of
distilled water were added and thoroughly stirred, and injected into a stirring water
bath. Using a laser diffraction particle size distribution analyzer, the light intensity
distribution was measured 64 times at intervals of 2 seconds, the particle size distribution
data was analyzed, and the particle size having a cumulative frequency distribution
of 50% (D50) was recorded as the average particle size. In addition, as a result of
the observation using an electron microscope, it was found that the proportion of
the primary particles (primary particles which are present alone and does not compose
secondary particles) in the negative electrode active material is 20% in terms of
the volume ratio, and that the average particle size of the primary particles is 0.6
µm.
[0091] The slurry thus obtained was applied to an aluminum foil collector having a purity
of 99% by weight, dried, and then the collector was pressed (pressing force: 0.12
ton/mm), thereby making a negative electrode having an electrode density of 2.1 g/cm
3. On the other hand, the thickness of the negative electrode current collector Ln
was 16 µm from the microscopic image of a cross section of the electrode photographed
by an electron microscope. The thickness of the negative electrode active material
containing layer was 45 µm.
[0092] On the other hand, the weight of the negative electrode active material containing
layer (NW) was 20 g. The charging capacity, which is obtained when the charging voltage
of the negative electrode is up to 1 V with reference to the Li potential (vs. Li/Li
+), per weight (NC) was calculated at 150 mAh/g using NW. The charging capacity when
the charging voltage of the negative electrode is up to 1 V with reference to the
Li potential (vs. Li/Li
+) was measured as described below.
[0093] A three-electrode cell including a working electrode of 2 cm × 2 cm cut out from
a negative electrode, a reference electrode of an Li metal strip, and a counter electrode
of Li metal foil (2.1 cm × 2.1 cm) was made. The charging capacity (Ah) when the potential
of the working electrode reached 1 V relative to the reference electrode by charging
at a rate of 0.1 C (Li absorbing reaction) was measured, the value was divided by
the weight NW (g) of the negative electrode active material containing layer in the
working electrode, and the value was recorded as the charging capacity per weight
NC.
[0094] The density of the negative electrode was measured as follows.
[0095] A negative electrode coated with slurry on both sides was cut out into a piece of
5 cm × 5 cm, and the total weight and thickness of the electrode were measured. Subsequently,
the negative electrode active material containing layer was removed from both sides
of the negative electrode using acetone, the weight and thickness of the collector
were measured, and the negative electrode density ρ (g/cm
3) was calculated by the formula (2):
wherein W
0 is the total electrode weight (g), W
1 the collector weight (g), T
0 is the electrode thickness (cm), T
1 is the collector thickness (cm), S is the negative electrode area, and 25 cm
2 in this case.
[0096] Alternatively, the negative electrode active material containing layer is removed
from the negative electrode thus made, the active material is separated from the negative
electrode active material containing layer using, for example, an organic solvent
or aqueous solution, and then the average particle size is determined in the same
manner as described above using the laser diffraction particle size distribution analyzer.
<Producing of positive electrode>
[0097] Lithium nickel cobalt manganese oxide (LiNi
0.5Co
0.2Mn
0.3O
2) powder having an average particle size of 5 µm as a positive electrode active material,
graphite powder as a conductive material, and polyvinylidene fluoride (PVdF) as a
binder were mixed at a weight ratio of 90 : 7 : 3, the mixture was dispersed in an
n-methylpyrrolidone (NMP) solvent to make a slurry. The slurry was applied to aluminum
foil (purity: 99.95% by weight), dried, and then the aluminum foil was pressed (pressing
force: 0.25 ton/mm), thereby making a positive electrode having an electrode density
of 3.3 g/cm
3. On the other hand, the thickness of the positive electrode current collector Ln
was 13 µm from the microscopic image of a cross section of the positive electrode
photographed by an electron microscope. The thickness of the positive electrode active
material containing layer was 30 µm.
[0098] The weight of the positive electrode active material containing layer (PW) was 25
g. The charging capacity per weight when the maximum charging voltage of the positive
electrode is up to 4 V (PC4) with reference to the Li potential (vs. Li/Li
+) was calculated at 125 mAh/g using PW. The charging capacity when the maximum charging
voltage of the positive electrode was up to 4V with reference to the Li potential
(vs. Li/Li
+) was measured as follows.
[0099] A three-electrode cell including a working electrode of 2 cm × 2 cm cut out from
a positive electrode, a reference electrode of an Li metal strip, and a counter electrode
of Li metal foil (2.1 cm × 2.1 cm) was made. The charging capacity (Ah) when the potential
of the working electrode reached 4 V relative to the reference electrode by charging
at a rate of 0.1 C (Li releasing reaction) was measured, the value was divided by
the weight PW (g) of the positive electrode active material containing layer in the
working electrode, and the value was recorded as the charging capacity per weight
PC4.
[0100] As the material for forming the container (cladding member), a laminate film having
a thickness of 0.1 mm and including an aluminum layer and a resin layer was provided.
The aluminum layer of the aluminum laminate film is about 0.03 mm. The resin reinforcing
the aluminum layer was polypropylene. The laminate film was bonded by heat sealing,
thereby obtaining a container (cladding member).
[0101] Subsequently, a laminated electrode group including a separator made of polyethylene
porous film having a thickness of 12 µm arranged between a plurality of positive electrodes
and a plurality of negative electrodes was made. A plurality of positive electrode
current collectors were electrically connected to a positive electrode terminal strip,
and a plurality of negative electrode current collectors were electrically connected
to a negative electrode terminal strip. The electrode group was inserted into a container
(cladding member).
[0102] A lithium salt LiPF
6 was dissolved at a concentration of 1.5 mol/L in an organic solvent, which had been
prepared by mixing PC and DEC at a volume ratio of 2 : 1, thereby preparing a liquid
nonaqueous electrolyte. The nonaqueous electrolyte thus obtained was injected into
a container, and a slim nonaqueous electrolyte secondary battery having the structure
shown in FIG. 1 was made, the laminate size (cup size) having a thickness of 6 mm,
a width of 70 mm, and a height of 110 mm.
(Examples 2 to 16)
[0103] Nonaqueous electrolyte secondary batteries were made in the same manner as in Example
1, except that the type of the negative electrode active material, the average particle
size of the secondary particles, the type of the positive electrode active material,
and Ln, Lp, NC,PC4, NC/PC4, and PW/NW were changed to the values shown in Table 1.
[0104] The Li absorbing potential of TiO
2 (B) in Table 1 was 1.3 V (vs. Li/Li
+), and the Li absorbing potential of Nb
2TiO
7 was 1.3 V (vs. Li/Li
+).
(Comparative Examples 1 to 7)
[0105] Nonaqueous electrolyte secondary batteries were made in the same manner as in Example
1, except that the type of the negative electrode active material, the average particle
size of the secondary particles, the type of the positive electrode active material,
and Ln, Lp, NC,PC4, NC/PC4, and PW/NW were changed to the values shown in Table 3.
In Table 3, "primary particles alone" means the absence of secondary particles. In
this case, the average particle size is the average particle size of the primary particles.
[0106] In Tables 1 and 3, for the parenthesized weight (g) in the column of PW/NW the left
value represents the weight of the positive electrode active material containing layer,
and the right value represents the weight of the negative electrode active material
containing layer.
[0107] The nonaqueous electrolyte secondary battery thus obtained was subjected to the following
two tests.
[0108] The first test was carried out as follows. In an environment at 80°C, the battery
was charged to 2.6 V at a constant current of 3 C, and then charged at a constant
voltage of 2.6 V, and the charge was finished when the current value reached 1/20
C. Thereafter, the battery was discharged to 1.5 V at 3 C. The charge and discharge
were repeated to carry out high temperature cycle test. The number of cycles when
the volume retention rate reached 80% was recorded as the cycle life.
[0109] The second test was high output discharge test and carried out as follows. In an
environment at 25°C, the battery was charged to 2.6 V at a constant current of 1 C,
and then charged at a constant voltage of 2.6 V, and the charge was finished when
the current value reached 1/20 C. Thereafter, the battery was discharged once to 1.5
V at a constant current of 10 C. The discharge capacity thus obtained was represented
by the value with the discharge capacity at 1 C as 100%, and the value is shown as
the 10C discharge retention rate in Tables 2 and 4. The discharge capacity shown in
Tables 2 and 4 is the discharge capacity at the time of discharge at 1 C.
[Table 1]
[0110]
Table 1
|
Negative electrode active material |
Secondary particle size (µm) |
Positive electrode active material |
Ln (µm) |
Lp (µm) |
NC (mAh/g) |
PC4 (mAh/g) |
NC/PC4 |
PW/NW |
Example 1 |
Li4/3Ti5/3O4 |
8 |
LiNi0.5Co0.2Mn0.3O2 |
16 |
13 |
150 |
125 |
1.2 |
1.25(25g/20g) |
Example 2 |
Li4/3Ti5/3O4 |
10 |
LiNi0.5Co0.2Mn0.3O2 |
17 |
13 |
150 |
125 |
1.2 |
1.25(25g/20g) |
Example 3 |
Li4/3Ti5/3O4 |
6 |
LiNi0.5Co0.2Mn0.3O2 |
15 |
13 |
150 |
125 |
1.2 |
1.25(25g/20g) |
Example 4 |
Li4/3Ti5/3O4 |
15 |
LiNi0.5Co0.2Mn0.3O2 |
17 |
13 |
150 |
125 |
1.2 |
1.25(25g/20g) |
Example 5 |
Li4/3Ti5/3O4 |
20 |
LiNi0.5Co0.2Mn0.3O2 |
17 |
8 |
150 |
125 |
1.2 |
1.25(25g/20g) |
Example 6 |
Li4/3Ti5/3O4 |
8 |
LiNi0.5Co0.2Mn0.3O2 |
16 |
10 |
150 |
125 |
1.2 |
1.25(25g/20g) |
Example 7 |
Li4/3Ti5/3O4 |
8 |
LiNi0.5Co0.2Mn0.3O2 |
16 |
15 |
150 |
125 |
1.2 |
1.25(25g/20g) |
Example 8 |
Li4/3Ti5/3O4 |
8 |
LiNi0.8Co0.1Mn0.1O2 |
16 |
13 |
150 |
130 |
1.15 |
1.20(24g/20g) |
Example 9 |
Li4/3Ti5/3O4 |
8 |
LiNi1/3Co1/3Mn1/3O2 |
16 |
13 |
150 |
120 |
1.25 |
1.30(26g/20g) |
Example 10 |
Li4/3Ti5/3O4 |
8 |
LiNi0.8Co0.15Al0.05O2 |
16 |
13 |
150 |
130 |
1.15 |
1.20(24g/20g) |
Example 11 |
Li4/3Ti5/3O4 |
8 |
LiFePO4 |
16 |
13 |
150 |
140 |
1.07 |
1.12(19g/17g) |
Example 12 |
Li4/3Ti5/3O4 |
8 |
LiFeSO4F |
16 |
13 |
150 |
130 |
1.15 |
1.18(20g/17g) |
Example 13 |
TIO2(B) |
15 |
LiNi0.5Co0.2Mn0.3O2 |
16 |
13 |
200 |
125 |
1.6 |
1.87(28g/15g) |
Example 14 |
Nb2TiO7 |
15 |
LiNi0.5Co0.2Mn0.3O2 |
16 |
13 |
220 |
125 |
1.76 |
2.23(29g/13g) |
Example 15 |
Nb2TiO7 |
8 |
LiNi0.5Co0.2Mn0.3O2 |
15 |
13 |
220 |
125 |
1.76 |
2.23(29g/13g) |
Example 16 |
Nb2TiO7 |
8 |
LiNi0.8Co0.1Mn0.1O2 |
15 |
13 |
220 |
130 |
1.69 |
2.3(30g/13g) |
[Table 2]
[0111]
Table 2
|
Discharge capacity (Ah) |
10C discharge capacity retention rate (%) |
80°C cycle life (time) |
Example 1 |
3 |
85 |
1200 |
Example 2 |
3 |
75 |
1500 |
Example 3 |
2.9 |
70 |
1000 |
Example 4 |
2.95 |
70 |
1800 |
Example 5 |
2.8 |
65 |
2000 |
Example 6 |
3 |
90 |
1400 |
Example 7 |
3 |
80 |
1000 |
Example 8 |
3.2 |
80 |
1200 |
Example 9 |
2.8 |
90 |
1500 |
Example 10 |
3.3 |
80 |
1000 |
Example 11 |
2.5 |
80 |
5000 |
Example 12 |
2.4 |
65 |
3000 |
Example 13 |
3.3 |
70 |
1100 |
Example 14 |
3.5 |
80 |
1200 |
Example 15 |
3.5 |
83 |
1100 |
Example 16 |
3.6 |
83 |
1000 |
[Table 3]
[0112]
Table 3
|
Negative electrode active material |
Secondary particle size (µm) |
Positive electrode active material |
Ln (µm) |
Lp (µm) |
NC (mAh/g) |
PC4 (mAh/g) |
NC/PC4 |
PW/NW |
Comparative Example 1 |
Li4/3Ti5/3O4 |
10 |
LiNi0.5Co0.2Mn0.3O2 |
10 |
15 |
150 |
125 |
1.2 |
1.25(25g/20g) |
Comparative Example 2 |
Li4/3Ti5/3O4 |
1 |
LiNi0.5Co0.2Mn0.3O2 |
16 |
13 |
150 |
125 |
1.2 |
1.25(25g/20g) |
Comparative Example 3 |
Li4/3Ti5/3O4 |
Primary particles alone, 0.3 µm |
LiNi0.5Co0.2Mn0.3O2 |
10 |
13 |
150 |
125 |
1.2 |
1.15(23g/20g) |
Comparative Example 4 |
Li4/3Ti5/3O4 |
Primary particles alone, 0.5 µm |
LiNi0.5Co0.2Mn0.3O2 |
10 |
13 |
150 |
125 |
1.2 |
1.15(23g/20g) |
Comparative Example 5 |
Li4/3Ti5/3O4 |
Primary particles alone, 1 µm |
LiNi0.5Co0.2Mn0.3O2 |
10 |
13 |
150 |
125 |
1.2 |
1.15(23g/20g) |
Comparative Example 6 |
Li4/3Ti5/3O4 |
Primary particles alone, 5 µm |
LiNi0.5Co0.2Mn0.3O2 |
10 |
13 |
150 |
125 |
1.2 |
1.15(23g/20g) |
Comparative Example 7 |
Li4/3Ti5/3O4 |
5 |
LiNi0.5Co0.2Mn0.3O2 |
8 |
13 |
150 |
125 |
1.2 |
1.15(23g/20g) |
[Table 4]
[0113]
Table 4
|
Discharge capacity (Ah) |
10C discharge capacity retention rate (%) |
80°C cycle life (time) |
Comparative Example 1 |
2.8 |
55 |
500 |
Comparative Example 2 |
2.5 |
50 |
600 |
Comparative Example 3 |
3 |
75 |
300 |
Comparative Example 4 |
3 |
75 |
200 |
Comparative Example 5 |
3 |
60 |
300 |
Comparative Example 6 |
3 |
50 |
400 |
Comparative Example 7 |
3 |
40 |
300 |
[0114] As shown in Table 1, the nonaqueous electrolyte secondary batteries of Examples 1
to 16 satisfy the relationship represented by the formula (2). As is evident from
Tables 1 to 4, the nonaqueous electrolyte secondary batteries of Examples 1 to 16
have higher high temperature cycke performance than Comparative Examples 1 to 7.
[0115] For the average particle size of the secondary particles of titanium-containing oxide
particles, the 80°C cycle life of the batteries of Examples 1, 2, 4, and 5 having
an average particle size of 7 to 20 µm is higher than that of Example 3 having an
average particle size of less than 7 µm, and the high temperature cycle performance
is improved when the average particle size is from 7 to 20 µm.
[0116] For the constitution of the positive electrode active material, comparison of Examples
1 and 10 indicates that the battery of Example 1 is superior to that of Example 10
in the discharge capacity, 10 C discharge retention rate, and 80°C cycle life. The
use of a lithium nickel cobalt manganese composite oxide improves the discharge capacity,
large current discharge performance, and high temperature cycle performance. In addition,
Example 11 using olivine lithium iron phosphate showed the highest 80°C cycle life.
[0117] The 80°C cycle life did not reach 1000 cycle in Comparative Example 1 wherein the
secondary particle size is higher than 5 µm but the Lp is thick, Comparative Example
2 wherein the Lp is thin, but the secondary particle size is less than 5 µm, Comparative
Examples 3 to 6 wherein the primary particles were used alone, and Comparative Example
7 wherein the secondary particle size is 5 µm and Lp is thick.
[0118] In addition, a battery module including a unit composed of six pieces of the nonaqueous
electrolyte secondary battery of each example, which are electrically connected in
series, can repeat charge-discharge cycles in a wide environmental temperature range
(for example -30°C to 80°C) at the maximum voltage of 15 V and minimum voltage of
8 V, so that showed marked compatibility with the operating voltage range of lead
storage batteries and parallel operation with lead storage batteries.
[0119] The nonaqueous electrolyte battery according to at least one embodiment and example
provides marked high rate charge-discharge cycle life performance and large current
discharge performance at high temperatures, because the battery includes a negative
electrode containing titanium-containing oxide particles having an average secondary
particle size of more than 5 µm, and the thickness of the positive electrode current
collector is smaller than the thickness of the negative electrode current collector.